The invention concerns a method and apparatus for balancing a vehicle wheel such as a motor vehicle wheel, more especially comprising a pneumatic tire and a disk wheel on which the tire is fitted.
In a method and an apparatus for balancing a motor vehicle wheel, as can be found in DE 42 29 865 C2 or DE 44 32 016 A1, the motor vehicle wheel is clamped on a measuring spindle of a balancing machine. The geometrical data of the wheel are mechanically sensed and stored and an unbalance is ascertained in at least one measuring run. The procedure involves calculating therefrom a balancing vector for the balancing mass and the balancing position in accordance with a balancing program which is selected in dependence on the disk wheel type and material, in at least one balancing plane on the motor vehicle wheel, and at least one balancing weight is fixed to the motor vehicle wheel in dependence on the balancing vector to compensate for the ascertained unbalance.
Conventional balancing machines, for example the Geodyna 5000 or Geodyna 5500 machines, see the prospectus from Hofmann Werkstatt-Technik GmbH, Pfungstadt Germany, imprint 950210103.94, have various balancing programs. The positioning of the balancing weights on the disk wheel can be determined by such balancing programs. Usually there is a standard program or normal program for disk wheels consisting of steel and five selectable balancing programs for disk wheels comprising light metal or alloy, in particular aluminum or aluminum alloy. That ensures that, depending on the type of disk wheel involved, the balancing weights are positioned on the wheel in consideration of the requirements for optimum smoothness of operation and visual appearance of the wheel, when carrying out the unbalance compensating operation.
An object of the invention is to provide a method of balancing a motor vehicle wheel in which the operating comfort and convenience when setting the machine to the type of wheel to be balanced is improved.
Another object of the invention is to provide a wheel balancing method which affords a combined procedure that brings together a number of operational aspects involved in balancing the wheel, in a reliable and readily implementable fashion.
Still another object of the invention is to provide an apparatus for balancing a motor vehicle wheel, which is of such a design as to facilitate the balancing operation and thus relieve operator stress.
Yet another object of the invention is to provide an apparatus for balancing a motor vehicle wheel, which permits the attainment of an enhanced degree of automation of operation.
In accordance with the invention, in regard to the method the foregoing and other objects are attained by a method of balancing a motor vehicle wheel comprising a pneumatic tire and a disk wheel, wherein the motor vehicle wheel is clamped on a measuring spindle of a balancing machine and the geometrical data of the wheel are sensed and stored. An unbalance of the vehicle wheel is ascertained in at least one measuring run and at least one balancing vector for the balancing mass and the balancing position is calculated in accordance with a balancing program selected in dependence on the disk wheel type and disk wheel material, in at least one balancing plane on the motor vehicle wheel. At least one balancing weight is fixed to the motor vehicle wheel in dependence on the balancing vector for compensation of the unbalance ascertained. When sensing the rim of the disk wheel, sensor means are used to detect whether a rim flange portion extending substantially perpendicularly to the measuring spindle is or is not present in the rim region being sensed; and in the rim-sensing operation detection of the material of the disk wheel is also effected, and a corresponding signal is produced. The balancing program is selected in dependence on the signals produced in the rim-sensing operation and the material-sensing operation.
In accordance with the invention in regard to the apparatus the foregoing and other objects are attained by apparatus for sensing a rim of a motor vehicle wheel which in operation of the apparatus is clamped on a measuring spindle of a balancing machine, comprising a sensing member which is mounted pivotably and extendably at the balancing machine and which has a sensing head. The sensing head carries a sensor responsive to a rim portion such as a rim flange which extends substantially perpendicularly to the axis of the measuring spindle.
Further in accordance with the invention and the apparatus aspect thereof the foregoing and other objects are attained by apparatus for balancing a motor vehicle wheel comprising a pneumatic tire and a disk wheel, including a measuring spindle for mounting the motor vehicle wheel, at least one sensing device for sensing geometrical data of the wheel, a storage means for storage of the geometrical data of the wheel, measuring means connected to the measuring spindle and operable in a measuring run to produce measuring signals are proportional to a wheel unbalance, an electronic machine system including an electronic evaluation arrangement and a plane computer and operable to calculate a balancing vector in dependence on the measurement values and the stored geometrical data of the wheel and a balancing program selected in dependence on the disk wheel type and disk wheel material, in at least one balancing plane on the wheel, wherein the sensing device includes at least one sensor by which a rim flange of the disk wheel can be detected and which is connected to the electronic evaluation arrangement, and wherein the electronic evaluation arrangement has a selection device operable to determine the balancing program in dependence on the sensed geometrical data of the wheel and the signal supplied by the sensor.
As will be seen in greater detail from the description hereinafter of preferred embodiments the invention provides that a rim of a disk wheel of a motor vehicle wheel is sensed by means of a preferably extendable sensing or feeler device. That involves ascertaining geometrical data such as radius or diameter and spacing of the rim in relation to the measuring shaft or spindle and measurement units which are influenced by the measuring spindle and which are connected to the electronic evaluation arrangement. Signals corresponding to the geometrical data ascertained in that way are passed to the electronic evaluation arrangement and possibly stored.
When mechanically sensing a rim region of the wheel, the axial spacing of which from the frame of the machine or the measurement units approximately corresponds to the axial spacing of a balancing plane, the procedure involves detecting by sensor means, for example by means of a sensor associated with the respective mechanical sensing or feeler device, whether a rim portion which extends at least substantially perpendicularly to the measuring spindle, in particular one of the two rim flanges, is or is not present in the rim region which is being sensed. In dependence on the signal obtained by the sensor means in that sensing operation, and the geometrical data ascertained in the mechanical sensing procedure, the balancing program is then selected or at least some of the programs which can be considered for the unbalance compensating operation are selected from the plurality of available balancing programs.
If the material of the disk wheel cannot be readily established, for example by visual inspection, then the mechanical sensing operation further involves detecting and recognising the material of the disk wheel and producing a corresponding signal, as is described in U.S. Pat. No. 5,983,717 (application Ser. No. 08/996,393), to which reference is accordingly directed for incorporation thereof. In dependence thereon and the result obtained in the rim region sensing operation, a further selection is then made in respect of the balancing programs available for compensating for unbalance, and the appropriate balancing program is selected. The electronic evaluation arrangement is then set to the appropriate type of wheel. In addition in that case also the choice of balancing program is dependent on the distance or the spacing of the sensed region or the balancing plane from the frame of the machine or from the measurement units or a representative reference plane which extends perpendicularly to the axis of the measuring spindle.
For the purposes of producing the signals by sensor means, a sensor can be arranged in the sensing or feeler head of a respective mechanical sensing member, for example a sensing bar of a sensing device. That makes it possible to detect whether the sensing head is disposed in a rim region in which there is a suitable rim portion, in particular a rim flange, that extends substantially perpendicular to the axis of the measuring spindle. That makes it possible to detect whether the sensing head is or is not bearing against the rim flange in the sensing operation. If the sensing head is disposed in the region of the base of the rim flange which extends approximately parallel to the wheel axis or further inwardly in the concealed inner region of the inward side of the rim (rim bed or bowl) in the sensing operation, the sensor does not detect a rim portion which extends perpendicularly to the measuring spindle. For example in the first case in which the rim flange is detected by the sensor, a corresponding signal at a given level can be outputted. If the rim flange is not detected by the sensor, the sensor can output a zero signal, no signal or a signal at another level.
Besides the conventional steel and light metal or alloy rims, also available on the market are disk wheels comprising light metal or alloy plate, in particular consisting of aluminum. The visual appearance of those disk wheels comprising light metal or alloy and in particular aluminum plate is substantially the same as the visual appearance of disk wheels consisting of steel plate. Particularly if the light metal or alloy and in particular aluminum plate disk wheels are painted with the same usual colour, which is generally black, as disk wheels of steel plate, major difficulties are often involved in ascertaining the correct material of the disk wheel and the correct choice of balancing weights, just on the basis of visual judgment. When fitting weights to one or both rim flanges of disk wheels of light metal or alloy plate, it is necessary to use special weights, for example clip-type weights, which do not damage the rim at the rim flange when they are fitted. Furthermore to avoid corrosion it is necessary for the weights to have a coating of suitable plastic material or of the same material as the light metal or alloy plate rim.
Preferably therefore the sensor is of such a nature that it can also detect the material of the disk wheel and in particular the rim thereof. In that respect, the sensor, as is described in above-mentioned U.S. Pat. No. 5,983,717 (application Ser. No. 08/996,393) distinguishes whether the disk wheel or the rim comprises a non-ferromagnetic material, for example aluminum, magnesium or titanium or alloys or mixed alloys thereof, or whether it comprises a ferromagnetic material, in particular steel. For that purpose the sensor can be in the form of an inductive proximity sensor whose magnetic field lines preferably issue approximately parallel or at an acute angle relative to the axis of the measuring spindle. The magnetic field lines are not only influenced when the sensor approaches a rim portion extending substantially perpendicularly to the measuring spindle, in particular a rim flange, but also they are influenced by the rim material. The sensor which is preferably in the form of an inductive proximity initiator or switch can be connected to an oscillator circuit whose oscillations, in particular frequency, are varied in dependence on the influencing of the magnetic field lines. It is further possible in that way to detect whether the rim material is a light metal or alloy or a ferromagnetic material, in particular steel. A particularly suitable sensor is a sensor which is responsive to ferromagnetic material and which can be of such a design that it responds only to ferromagnetic material. It is possible for that purpose to use the above-mentioned inductive proximity switch or initiator (see for example xe2x80x98Elektrotechnikxe2x80x99 57, issue 24, Dec. 7, 1975, pages 39-42). Further suitable sensors are capacitive proximity switch, optical reflection switches, microswitches and the like.
In addition the sensing head in accordance with the invention can be of such a configuration that the dimension and in particular width of a balancing weight which is fitted into the sensing device is determined by sensor feeler sensing, for example by means of a separate sensor or by means of the sensor which provides for sensing the rim flange and/or the material involved. For that purpose the sensing head has a weight-holding device as is to be found in DE 41 43 623 to which reference is made to incorporate the disclosure thereof. By virtue of that sensing procedure, it is possible to detect whether the holding device is in the rest position or whether a weight and more particularly an adhesive weight is fitted into the sensing head or the holding device. In that way it is possible to achieve an improvement in the degree of accuracy involved in positioning the weight in the balancing operation. In particular it is possible in that respect to take account of the position of the center of gravity of the balancing weight (see DE 27 37 524 A1). It is also possible to detect from the signal outputted by the sensor whether an adhesive weight is fitted in the holding device and/or what the width of the weight is. Those signals can also be used for determining the balancing program and thus for setting the electronic evaluation arrangement to the appropriate type of wheel. For that purpose the sensor can be in the form of a travel measuring device which determines the position of the weight-holding device, in particular a spring-loaded holding portion of the weight-holding device (see DE 42 29 865 C2).
The electric lines with which the sensor signals are passed to the electronic evaluation arrangement can be secured by way of a flexible pull or traction element, for example a band or toothed belt, which serves to determine the extension length of the sensing member, as in EP 0 694 775 A2 to which reference is directed. That flexible pull element is connected to the sensing head and can be passed by the telescopically extendable sensing member such as for example a sensing bar to a roller which is acted upon by a drive spring to hold the pull element and in particular the toothed belt taut. The flexible pull element can also be used in known manner for limiting extension of the sensing head provided with the weight-holding device, as for example when a balancing position is reached in the balancing procedure. It is possible for that purpose to use a blocking device such as for example a clamping device as is known for example from EP 0 694 775 A2.
For feeding the operating voltage to the sensor and for the signal lines, it is also possible to employ a flexible circuit board which is passed along the flexible pull element.
Further objects, features and advantages of the invention will be apparent from the following description of preferred embodiments.